1. Field of the Invention
The present invention relates to a capacitance type sensor suitably used for detecting a force applied from outside.
2. Description of the Related Art
A capacitance type sensor is in general use as a device for converting magnitude and direction of a force applied by an operator into electric signal. For example, a device having the capacitance type sensor for inputting operation of multidimensional direction incorporated as a so-called joystick is used as an input device of a mobile phone.
A capacitance type sensor can be used to input an operation having a specified dynamic range as a magnitude of a force applied by an operator. Among others, a capacitance type force sensor having a capacitance element formed by two electrodes to detect an applied force on the bags of changes of capacitance values caused by variations of distance between the electrodes is now in practical use in a variety of fields in terms of the advantage that the structure can be simplified to reduce costs.
For example, Japanese Laid-open (Unexamined) Patent Publication No. Hei 7(1995)-200164 discloses a capacitance type sensor 510 as shown in FIG. 21. The capacitance type sensor 510 has a substrate 520, an elastic rubber plate 530 disposed over the substrate 520, an electrode part 540 disposed on a lower surface of the elastic rubber plate 530, an electrode part 500-504 arranged on an upper surface of the substrate 520 (See FIG. 22), a presser plate 560 for fixedly supporting the elastic rubber plate 530 to the substrate 520, and an electronic device 580 arranged on a lower surface of the substrate 520. The electrode part 500-604 comprises electrodes part 501, 502 arranged to be symmetric with respect to the Y-axis, electrodes part 503, 504 arranged to be symmetric with respect to the X-axis, and an annular electrode part 500 arranged around the outside of those electrodes part. The periphery of the electrode part 540 is in contact with the electrode part 500 connected to ground and thus is connected to ground through the electrode part 500.
When an operator presses down the elastic rubber plate 530, the electrode part 540 is displaced downwardly increasingly with the displacement force, so that the distances between the electrode part 540 and the four electrodes part 501-504 are changed. Then, the capacitance values of the capacitance elements formed between the four electrodes part 501-504 and the electrode part 540 are changed. By detecting the changes of the capacitance values, magnitude and direction of a force applied by the operator can be recognized.
This capacitance type sensor 510 is suitably used for a device that can detect magnitude of a force applied by the operator when pressing down the elastic rubber plate 530, but is not suitable for a device having the switch function of selectively switching between two different modes (e.g. on-state and off-state). Accordingly, when this capacitance type sensor is built in equipment as a device having a multidirectional switch function, the capacitance type sensor can hardly be used as it is and is required to add switch functions corresponding to the respective directions.
It is an object of the present invention to provide a capacitance type sensor applicable to either of a device for sensing magnitude of a force for each direction and a device having switch function.
In accordance with the first aspect of the present invention, there is provided a capacitance type sensor comprising a detective member, a first electrode being opposite to the detective member, a second electrode arranged between the detective member and the first electrode and constituting capacitance elements with the first electrode, the second electrode being displaceable in a same direction as the detective member when the detective member is displaced, one or more first switching electrodes being opposite to the detective member, and one or more second switching electrodes arranged between the detective member and the first switching electrode(s) in such a relation as to be opposite to the first switching electrode(s) and also spaced apart from the first switching electrodes), the second switching electrodes being contactable with the first switching electrodes increasingly with displacement of the detective member, wherein the first and second switching electrodes are arranged to overlap with the first and second electrodes with respect to a displacement direction of the detecting member, and wherein the capacitance type sensor is capable of recognizing the displacement of the detective member on the basis of a detection, using a signal input to the first electrode, of a change in capacitance value of the capacitance element caused by a change in distance between the first electrode and the second electrode.
According to this construction, since displacement of the detective member is recognized by detecting variations of the capacitance values of the capacitance elements caused by changes in distance between the first electrode and the second electrode, magnitude of a force applied to the detective member from outside can be recognized. Also, since contact of the first switching electrodes with the second switching electrodes) can be recognized, this can be used as the switching function. Accordingly, the capacitance type sensor of the invention can be used as a device having the function of outputting the displacement of the detective member (the magnitude of a force applied to the detective member from outside) in the form of signal (analog signal) and/or a device having the switch function. Thus, this capacitance type sensor has the function as a composite device useable as either of the former device and the latter device, so that the need to re-create the sensor for either of the purposes mentioned above is eliminated.
The first and second switching electrodes and the first and second electrodes are arranged to overlap with each other with respect to the displacement direction of the detective member (arranged in two layers with respect to a vertical direction, for example). This can practically solve the problem, involved in the arrangement wherein the first and second switching electrodes are disposed in a plane substantially common with the first and second electrodes, that due to the first and second switching electrodes being disposed inside of the first electrode or the second electrode, an effective area for the first electrode or the second electrode is reduced, causing significant reduction in sensitivity of the capacitance type sensor. This can also solve the problem that due to the first and second switching electrodes being disposed outside of the first electrode or the second electrode, a relatively large area is required for placement of the electrodes included in the sensor, causing increase in size of the sensor.
The expression that xe2x80x9cdisplacement of the detective member can be recognizedxe2x80x9d has substantially the same meaning as the expression that xe2x80x9ca force applied to the detective member from outsidexe2x80x9d.
The capacitance type sensor of the present invention may further comprise a first substrate disposed on the side opposite to the second electrode with respect to the first electrode and having the first electrode on its surface, a second substrate disposed on the side opposite to the first electrode with respect to the second electrode and having the second electrode on its surface, a first switching substrate disposed on the side opposite to the second switching electrode(s) with respect to the first switching electrodes and having the first switching electrodes on its surface, and a second switching substrate disposed on the side opposite to the first switching electrode(s) with respect to the second switching electrodes and having the second switching electrodes on its surface. According to this construction, since the first and second electrodes and the first and second switching electrodes are arranged on the substrate, those electrodes can be set in proper position on the substrate easily, thus providing simplified production process of the sensor.
In the capacitance type sensor of the present invention, the first substrate, the second substrate, the first switching substrate and the second switching substrate may be formed by a single common substrate having flexibility. According to this construction, the sensor is produced by arranging the respective electrodes on a single common substrate, first, and, then, folding the common substrate. This can provide simplified production process of the sensor. In addition, since the sensor unit of the sensor of the present invention is formed as a unit (unitized), even when appearance of the sensor or the detecting part is modified, a commonly available sensor unit can be obtained. Further, in this case, since the sensor unit can be placed on a circuit board on which for example a circuit pattern (wiring) is formed, an effective wiring area of the circuit board need not be reduced.
In the capacitance type sensor of the present invention, the first electrode, the second electrode, the first switching electrode, and the second switching electrode may be all arranged on one side of the common substrate. According to this construction, since all the electrodes are arranged on the common substrate, the production process of the sensor can be simplified further and the production costs can be reduced further.
In the capacitance type sensor of the present invention, the first and second switching electrodes may be disposed to be doser to the detective member than the first and second electrodes. According to this construction, the distance between the first switching electrode and the second switching electrode can be changed easily before the distance between the first electrode and the second electrode changes, which is preferable when the switch function of switching between the first switching electrode and the second switching electrode is given priority use.
In the capacitance type sensor of the present invention, there are provided two or more groups of the first and second electrodes or two or more groups of the first and second switching electrodes. According to this construction, the capacitance type sensor can be used as a device having the function of recognizing a multidimensional force and/or a device having the switch function by using the respective groups to recognize forces for different directions.